Stability constants and decay of aqua-copper(III) - A study by pulse radiolysis with conductometric and optical detection

Hydroxyl radicals were generated radiolytically in N2O-saturated aqueous so lutions and reacted with Cu-aq(2+) ions. Pulse radiolysis with conductometr ic detection showed that the aqua-Cu-III species thus formed (k = 3.2 x 10( 8) dm(3) mol(-1) s(-1)) is uncharged at pH 5, i.e. [Cu(OH)(3)](aq), and fro m the changes in conductance as a function of pH it has been calculated tha t Cu(OH)(2)(aq+) must have a pK value of 4.8 and Cu(OH)(aq)(2+) a value of 3.7. At pH 2.5 there is no strong evidence for the presence of Cu-aq(3+). A qua-Cu(OH)(3) decays bimolecularly to give Cu-aq(2+) and H2O2. Cu(OH)(aq)(2 +) [and possibly also Cu(OH)3,,] are in equilibrium with Cu-aq(2+) and OH r adicals [K(Cu(OH)(aq)(2+)) approximate to 3.7 x 10(4) dm(3) mol(-1)]. Rapid electron transfer occurs from Cu-aq(+) to [Cu(OH)(3)](aq) (k = 3.5 x 10(9) dm(3) mol(-1) s(-1)).